Can I Use 2-Cycle Gas in My 4-Cycle Mower?

Two-Cycle Engines

• Two-cycle engines exist on smaller, lightweight -- and most often -- hand-held power tools. These engines have fewer moving parts and weigh less, while still delivering a considerable amount power to the external moving parts. Further reducing their design and weight, these engines don’t use an oil pump to distribute lubrication throughout the piston and the crankshaft. Lubrication instead comes from the fuel. An operator mixes oil specially designed for two-cycle engines directly into the gas for delivery to the combustion chamber.

Four-Cycle Combustion

• Four-cycle engines usually get installed on slightly larger power tools and outdoor equipment. These engines are more powerful, as they have two pistons instead of one, and are usually much heavier than their counterparts. These engines also have a separate tank for oil and an oil pump that pushes oil into the crankcase during operation. Since the oil and gas are separate, the operator doesn’t need to mix fuel and will use the same gas that goes into cars or trucks.

Switching Fuels

• The oil inside the fuel of a two-cycle engine burns at a lower temperature than the straight gas used inside a four-cycle engine. When this fuel burns inside the combustion chamber of a four-cycle engine accustomed to straight gas, the engine’s performance will suffer. Also, a small amount of fuel will go unburned inside the chamber and leave behind a gummy buildup that can hinder normal operation of a four-cycle engine. Conversely, straight gas can never be used in a two-cycle engine, as it will burn too hot.

Tips and Recommendations

• When mixing two-cycle gas for use in two-cycle engines, the operator should only mix an amount that can be used in less time than 30 days. If this gas has sat for more than 30 days, the oil and gas will start separating. The gas will start destabilizing, which can damage a two- or a four-cycle engine. Any unused fuel at the end of the season needs to be disposed of according to local environmental regulations. Fuel shouldn’t be left inside two- and four-cycle engines getting stored for winter. Start and run the tools until all of the gas has been burnt off.